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SustainableSapphire

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atomic theory chemistry science physics

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This document discusses the historical development of atomic theory, from Democritus to modern models. The key figures and their contributions are highlighted, along with atomic structures and models.

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SCH 4U Unit 1 Structure and Properties of Matter Atomic Theory Democritus Hypothesized that if matter was cut into smaller and smaller pieces that at some point you cannot cut it into smaller pieces any more This smallest piece of matter was called the atom (indivisible) John Dalton S...

SCH 4U Unit 1 Structure and Properties of Matter Atomic Theory Democritus Hypothesized that if matter was cut into smaller and smaller pieces that at some point you cannot cut it into smaller pieces any more This smallest piece of matter was called the atom (indivisible) John Dalton Stated that all matter is composed of extremely small particles called atoms Atoms of one element are identical in size, mass, and chemical properties The atoms of a given element are different from the atoms of all other elements Atoms cannot be subdivided or destroyed (Billiard Ball Model) In chemical reactions, atoms are combined, separated, or rearranged Atoms of different elements can combine to form compounds which are always found in definite proportions (Law of Definite Proportions) J.J Thomspon Discovered negative electrons Atoms were made of positive material with negative electrons floating around within it (Plum-Pudding Model) Ernst Rutherford Discovered a dense positive piece at the center of the atom- nucleus that contained protons (Gold Foil Experiment) Electrons surrounded it (Nuclear Model) Atoms were mostly empty space Suggested that there must also be another particle found in the nucleus that was neutral that must also make up the mass of the atom (neutron) (1908 Nobel Prize in Chemistry) a particle velocity ~ 1.4 x 107 m/s (~5% speed of light) Origin of Quantum Theory Max Planck Observed that excited gases under low pressure produce a bright line spectra indicating that energy must be emitted only at specific wavelengths Proposed that molecules cannot absorb or emit any arbitrary amount of energy, but can absorb or emit energy in discrete (specific) quantities The name quantum was given to the smallest quantity of energy that can be absorbed or emitted Continuous Spectra H Line Spectra Ne Line Spectra Niels Bohr Hypothesized that an electron can circle the nucleus only in allowed paths (orbits)- Planetary Model An electron in any of these orbits has a definite amount of energy (quantized) Albert Einstein Explained the photoelectric effect (light striking metals eject electrons) Suggested that although light exhibited properties of a wave, it also was a stream of particles called photons Each photon possessed energy (E) If photons possesses enough energy (a specific quantity or quantum of energy), it will cause an electron to jump to a higher energy level Louis de Broglie Proposed that like light, electrons also exhibit a wave- particle nature Sometimes it behaved like a continuous electromagnetic wave, and sometimes it behaved like a definite particle Erwin Schrodinger His model described general orbital clouds in which electrons may be found Only the probability of finding an electron at a certain distance from the nucleus can be calculated The location of an electron cannot be pinpointed but only approximated in a general orbital cloud (Heisenberg’s Uncertainty Principle) This is because in order to measure the speed or position of an electron, we must hit it and change both its speed and direction Seatwork / Homework Read p. 143-146 Answer p.147 #1-3, 10 Read p.148-151 Answer p.152 #1, 3

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